The invention relates to a method and to a device for influencing relevant quality parameters of a rolled strip. More particularly, the invention relates to such a method and device that includes adjusting the crown of the rolls, the crown being the surface geometry of the rolls in the longitudinal direction of the rolls, by adjustably cooling the rolls or their surfaces in the longitudinal direction.
Hot rolled products with temperatures of between 800 and 1200xc2x0 C. cause noticeable heating and thereby thermal expansion of the work rolls. This results in what is known as a thermal crown of the work rolls, which directly influences thickness, thickness section profile, and flatness of the strip. These are important measures for the quality of the rolling process. The geometry of the strip cross-section is influenced by the geometry of the rolls in a roll stand, i.e., the crown of the rolls. It is known in the art to compensate thermal crown by suitable correction elements, such as screw down, bending force, etc. This method is effective, for instance, in so-called CVC [Continuously Variable Crown Rolls] or taper rolls. However, the preadjustment of CVC rolls is possible only in their unloaded state. They are consequently exclusively used for preadjustment. In addition, this method is extremely complex and costly and reduces the life of a roll stand.
If the adjustment reserves are insufficient, strip quality suffers.
One object of the invention is to define a method that makes it possible to influence the geometry of rolled strip in a simple manner. A further object of the invention is to provide a device that makes it possible to influence the geometry of rolled strip in a simple manner.
According to one formulation of the invention, these and other objects are attained by adjusting the crown of the rolls, the crown being the surface geometry of the rolls in a longitudinal direction of the rolls, by adjustably cooling the rolls or their surfaces in the longitudinal direction of the rolls, wherein the cooling of the rolls is adjusted with a controller as a function of an actual value of the crown and a predefined setpoint value of the crown. According to another formulation, the invention provides a device including an adjustable cooling apparatus to adjust the crown of the rolls, and a controller to adjust the cooling apparatus as a function of an actual value of the crown and a predefined setpoint value of the crown.
The relevant quality parameters of rolled strip, particularly the profile or flatness of rolled strip, in a roll stand with rolls are influenced by adjusting the crown of the rolls, i.e., the surface geometry of the rolls in longitudinal direction of the rolls. This adjustment of the crown of the rolls is achieved by adjustable cooling of the rolls, or their surface, in longitudinal direction of the rolls. The cooling of the rolls is adjusted by means of a controller as a function of an actual value of the crown and a predefined setpoint value of the crown.
The control algorithm of the controller is preferably a fuzzy logic algorithm.
According to an advantageous embodiment of the invention, anticipatory control with a view to the next rolled strip or, preferably, the next rolled strips, is achieved analogously to the method disclosed in German Patent DE 196 18 995 A1 and the corresponding U.S. Pat. No. 5,855,131 A. This is highly advantageous since the thermal crown reacts only sluggishly to the environment (water cooling) (controlled system with delay).
According to an advantageous embodiment of the invention, the thermal crown is adjusted in such a way that sufficient adjustment reserves of other (undelayed action) control variables regarding profile and flatness remain available. An associated roll pass schedule pre-calculation supplies the appropriate setpoints for the controller.